In an MBMS (Multimedia Broadcast Multicast Service) of a mobile communication system, data are delivered to a plurality of mobile terminals (UEs: User Equipments) by broadcast or multicast. Data are delivered according to the p-t-p (Point-to-Point) system or the p-t-m (Point-to-Multipoint) system. The p-t-p system is a one-to-one communication system, whereas the p-t-m system is a one-to-many communication system.
As regards the types of bearers over radio channels used for data communications, there are a bearer dedicated for the p-t-p communication (p-t-p bearer) and a bearer dedicated for the p-t-m communication (p-t-m bearer). In the MBMS, the type of bearer can be changed to the other type of bearer depending on the situation during the service.
The p-t-m bearer is established as a common channel over radio channels. Thus, if the p-t-m bearer is used, the common resources are consumed regardless of the number of UEs that receive a service. In contrast, the p-t-p bearer is established as a dedicated channel. Specifically, the p-t-p bearer is established as a dedicated transport channel (DTCH). Since a dedicated channel is set up for each UE, if the p-t-p bearer is used, the resources of dedicated channels corresponding to the number of UEs that receive a relevant service are consumed.
For example, if the number of UEs that requests to receive a particular MBMS service in a cell is 0 or very small, the case in which data are delivered to individual UEs using the dedicated p-t-p bearers consumes less radio resources than the case in which data are delivered to UEs using the common p-t-m bearer.
In contrast, if the number of UEs that request to receive a particular MBMS service in the cell is equal to or greater than a predetermined number, the case in which data are delivered using the p-t-m bearer consumes less radio resources than the case in which data are delivered using the dedicated p-t-p bearers. In addition, using the p-t-m bearer is advantageous to UEs. For example, while receiving an MBMS service through a common channel of the p-t-m bearer, a UE can perform another communication through a dedicated channel.
As described above, by properly selecting the p-t-p bearer or the p-t-m bearer for the MBMS service, the radio resources can be effectively used. To appropriately select the type of bearer, the standard specifications define a counting procedure that counts the number of UEs that requests to receive an MBMS. In addition, various techniques that accurately grasp the number of UEs that request to receive the MBMS have been proposed (for example, refer to JP2007-533217A (translation version)). The counting procedure is basically performed in such a manner that the network side makes inquiries for UEs and counts the number of UEs based on the responses therefrom.